This invention relates to hybrid spread spectrum methods and systems for wirelessly transmitting and receiving wideband digital data and, in particular, to spread spectrum methods and systems for wirelessly transmitting and receiving wideband digital data utilizing direct sequence and frequency hopping spectrum techniques.
Most interference, deliberate or accidental, affects communication because the information transmitted is condensed to a relatively small range of frequencies. An interference source active at the same frequency would produce signals that would mix with the actual communication channel to create errors. If, however, the information bearing signal is dispersed over a wider range of frequencies, the noise impulses can interference affect only a portion of the total information channel and can be filtered.
Spread spectrum technology increases the channel bandwidth of the signal to make it less vulnerable to interference. It refers to the transmission of a signal using a much wider bandwidth than would normally be required or to the use of narrow signals that are frequency-hopped through the various frequency segments available to the transponder. This approach is called spread spectrum multiple access (SSMA) or code-division multiple access (CDMA).
Spread spectrum technology was first adopted for military communication to prevent deliberate jamming or interference resulting from battle conditions. CDMA operates in three modes: direct sequence, frequency hopping, and time hopping.
For commercial applications, spread spectrum technology permits the use of small antennas (1.2 to 1.8 m in diameter). FCC regulations governing interference are related to power per unit bandwidth (power density). Either increasing the antenna size or the signal bandwidth would reduce the power density to acceptable levels. Rather than use a large antenna (which increases costs by a factor proportional to at least the square of the diameter), signal bandwidth is increased to reduce power density and, thus, interference.
With direct sequence spectrum spreading, transmitted information is mixed with a coded signal that, to an outside listener, sounds like noise. In this alternative to frequency hopping, each bit of data is sent at several different frequencies simultaneously, with both the transmitter and receiver synchronized, of course, to the same coded sequence.
More recently, further advances in chip technology have produced digital signal processors that can crunch data at high speed, use little power and are relatively inexpensive. The improved hardware allows more sophisticated spread-spectrum techniques, including hybrid ones that leverage the best features of frequency hopping and direct sequence, as well as other ways to code data. The new methods are particularly resistant to jamming, noise and multipathxe2x80x94a frequency-dependent effect in which a signal reflects off buildings, the earth and different atmospheric layers, introducing delays in the transmission that can confuse the receiver.
The U.S. patent to Ben-Efraim (U.S Pat. No. 5,630,212) provides for a microwave system with software configuration of operating parameters. Substantially all parameters in a radio are available and configurable using a network management system.
The U.S. patent to Monahan-Mitchell et al. (U.S Pat. No. 5,381,346) provides for a radio transceiver with a microcomputer which controls hardware dependent components. Software control of the microprocessor allows interaction with channel assignment, channel maintenance and other signaling.
The U.S. patent to Delprat et al. (U.S Pat. No. 5,583,870) provides for a cellular radio base station with software control of transceiver means.
The U.S. patent to Sandvos et al. (U.S Pat. No. 5,490,275) provides for a virtual radio interface and radio operating system for a communication device. A radio operating system is described which controls functioning of a radio through a MC68HC11 microcontroller.
The U.S. patent to Dunn et al. (U.S Pat. No. 5,625,877) provides for a wireless variable bandwidth air-link system. An apparatus which dynamically aggregates radio channels comprises a transceiver, microprocessor, and software.
The U.S. patent to Crosby (U.S Pat. No. 5,694,138) provides for a single coaxial cable which carries downlink signals from a satellite antenna and power signals to operate the antenna and an attached heating element.
The U.S. patent to Snow (U.S Pat. No. 4,115,778) provides for an electronic solid state FM dipole antenna. An amplified RF signal and DC power signal share a coaxial cable.
The U.S. patent to Mead (U.S Pat. No. 3,843,922) provides for a television preamplifier power source. The preamplifier is attached to an antenna mast and power is supplied through a coaxial cable which also transmits RF signals.
The U.S. patent to Dumbauld et al. (U.S Pat. No. 4,823,386) provides for a cable TV distribution system which uses a single coaxial cable to power subscriber frequency converters and carry video and control signals.
Other relevant U.S. patents include the U.S. Pat. Nos. 5,459,474 to Mattioli et al.; U.S Pat. No. 5,548,813 to Charas et al.; U.S Pat. No. 5,502,715 to Penny; and U.S Pat. No. 5,612,652 to Crosby.
The non-patent literature entitled xe2x80x9cWelcome to WIMANxe2x80x9d, describes a wireless MAN that allows an ISP to offer wireless Internet access.
The non-patent literature entitled xe2x80x9cBase Unit Systemsxe2x80x9d, lists Mikro-Tik wireless ISP routers and systems.
The non-patent literature entitled xe2x80x9cMicrocomm Digital Communication Productsxe2x80x9d, describes spread spectrum digital radio offerings and provides for an indoor/outdoor antenna unit to reduce cable loss. This literature appears on a web site.
An object of the present invention is to provide a hybrid spread spectrum method and system for wirelessly transmitting and receiving wideband digital data wherein channels can be quickly changed in a coordinated fashion so that multiple systems can be incorporated into networks without the fear of message collision between the different systems.
Another object of the present invention is to provide a hybrid spread spectrum method and system for wirelessly transmitting and receiving wideband digital data wherein the system includes an indoor unit and an outdoor unit with an antenna and wherein control, power and radio frequency signals are combined in a single cable run between the indoor and outdoor units, thereby eliminating the need for wide temperature range circuits in the outdoor unit.
In carrying out the above objects and other objects of the present invention, a hybrid spread spectrum method for wirelessly transmitting wideband digital data is provided. The method includes the steps of formatting the digital data based on a predetermined protocol and dynamically allocating bandwidth to the formatted digital data based on a predetermined set of conditions. The method also includes the steps of coding the formatted digital data with a signal to obtain encoded digital data and transmitting the encoded digital data at a plurality of different frequency bands, each of which has a center frequency so that each bit of digital data is sent at each of the different frequency bands substantially simultaneously. The method further includes the step of dynamically changing the center frequencies in real-time in less than 100 milliseconds.
Preferably, a hybrid spread spectrum method is provided for receiving wideband digital data by reversing the steps of the above method.
Further in carrying out the above objects and other objects of the present invention, a hybrid spread spectrum system for wirelessly transmitting wideband digital data is provided. The system includes means for formatting the digital data based on a predetermined protocol to obtain formatted digital data, means for dynamically allocating bandwidth to the formatted digital data based on a predetermined set of conditions, means for coding the formatted digital data with a signal to obtain encoded digital data, means for transmitting the encoded digital data at a plurality of different frequence bands, each of which has a center frequency so that each bit of digital data is sent at each of the different frequencies substantially simultaneously, and means for dynamically changing the center frequencies in real-time in less than 100 milliseconds.
A hybrid spread spectrum system for wirelessly receiving wideband encoded and formatted digital data is also provided to carry out the above objects and other objects of the invention. The system includes means for decoding the encoded formatted digital data with a signal to obtain decoded formatted digital data, means for deformatting the decoded formatted digital data based on a predetermined protocol to obtain the digital data, means for dynamically deallocating bandwidth to the encoded formatted digital data based on a predetermined set of conditions, means for receiving the wideband encoded, formatted digital data at a plurality of different frequency bands, each of which has a center frequency so that each bit of digital data is received at each of the different frequency bands substantially simultaneously, and means for dynamically changing the center frequencies in real-time in less than 100 milliseconds.
Further in carrying out the above objects and other objects of the present invention, in a hybrid spread spectrum system including an indoor unit and an outdoor unit for wirelessly transmitting and receiving wideband digital data, a method is provided for transmitting power, control and RF signals between the indoor and outdoor units. The method includes the steps of coupling a single coaxial cable between the indoor unit and the outdoor unit, and transmitting the control, power and RF signals between the indoor unit and the outdoor unit over the single coaxial cable.
The above objects and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.